查找有关MySQL中重复电子邮件的统计信息

Question

我需要查询有关数据库表中重复值的统计信息。例如，假设我有一个电子邮件字段，并且多行可以具有相同的电子邮件。我知道想知道重复多少次 多少次。换句话说：“908封电子邮件重复10次，1783封电子邮件重复9次”等等。

Repeated       # of Emails
10             908
9              1783

我不需要查看实际的电子邮件地址，只需要查看这些统计信息。

知道我有这个查询也检索电子邮件地址：

select email_address,
count(email_address) as NumberOccurrences
from table_user_info
group by email_address
having ( count(email_address) > 1 )

如何对这些结果进行分组？

Answer 1

带有子查询的聚合COUNT()也会返回聚合COUNT()。子查询对每个电子邮件地址进行分组和计数，如abc@example.com - 10中所示，然后外部查询按子查询返回的重复次数计数和分组，丢弃实际的电子邮件地址。

SELECT
  repeated,
  COUNT(*) AS numemails
FROM (
  SELECT 
     email,
     COUNT(*)
  FROM emails
  GROUP BY email
) emailcounts

Answer 2

select email_address,
       count(email_address) as NumberOccurrences
from table_user_info
group by email_address
having count(*) > 1